@vdux offers regular haiku contests which I also write for. That one is looking for the classic 5/7/5 total of 17 syllables. Very fun and lots of interesting voices.
Mizu no oto is a haiku contest by @bananafish. There's a Spanish edition and an English edition. The characteristics looked for in these haikus are stringent, and the allowable syllables are fewer.
Love them both.